Department of Ophthalmology and Visual Science, University of Texas Medical School at Houston, Houston, TX 77030, USA.
J Neurosci. 2012 Mar 28;32(13):4675-87. doi: 10.1523/JNEUROSCI.4749-11.2012.
Photoreceptors are coupled via gap junctions in many mammalian species. Cone-to-cone coupling is thought to improve sensitivity and signal-to-noise ratio, while rod-to-cone coupling provides an alternative rod pathway active under twilight or mesopic conditions (Smith et al., 1986; DeVries et al., 2002; Hornstein et al., 2005). Gap junctions are composed of connexins, and connexin36 (Cx36), the dominant neuronal connexin, is expressed in the outer plexiform layer. Primate (Macaca mulatta) cone pedicles, labeled with an antibody against cone arrestin (7G6) were connected by a network of fine processes called telodendria and, in double-labeled material, Cx36 plaques were located precisely at telodendrial contacts between cones, suggesting strongly they are Cx36 gap junctions. Each red/green cone made nonselective connections with neighboring red/green cones. In contrast, blue cone pedicles were smaller with relatively few short telodendria and they made only rare or equivocal Cx36 contacts with adjacent cones. There were also many smaller Cx36 plaques around the periphery of every cone pedicle and along a series of very fine telodendria that were too short to reach adjacent members of the cone pedicle mosaic. These small Cx36 plaques were closely aligned with nearly every rod spherule and may identify sites of rod-to-cone coupling, even though the identity of the rod connexin has not been established. We conclude that the matrix of cone telodendria is the substrate for photoreceptor coupling. Red/green cones were coupled indiscriminately but blue cones were rarely connected with other cones. All cone types, including blue cones, made gap junctions with surrounding rod spherules.
在许多哺乳动物物种中，光感受器通过缝隙连接相互耦联。人们认为，锥体细胞间的耦联可以提高灵敏度和信噪比，而视杆细胞与锥体细胞的耦联则为黄昏或中间光条件下的视杆细胞提供了一种替代途径（Smith 等人，1986 年；DeVries 等人，2002 年；Hornstein 等人，2005 年）。缝隙连接由连接蛋白组成，而连接蛋白 36（Cx36）是主要的神经元连接蛋白，在外丛状层中表达。用针对锥体抓捕蛋白（7G6）的抗体标记灵长类（猕猴）锥体足突，发现它们通过称为终末突的细过程网络相互连接，在双标记材料中，Cx36 斑精确地位于锥体之间的终末突接触处，强烈表明它们是 Cx36 缝隙连接。每个红/绿锥体与相邻的红/绿锥体形成非选择性连接。相比之下，蓝锥体足突较小，短终末突相对较少，与相邻锥体的 Cx36 接触也很少或不确定。在每个锥体足突的外围以及一系列非常短的终末突上也有许多较小的 Cx36 斑，这些终末突太短而无法到达锥体足突镶嵌的相邻成员。这些小的 Cx36 斑与几乎每个视杆小球紧密对齐，可能标识了视杆细胞与锥体细胞的耦联部位，尽管尚未确定视杆细胞连接蛋白的身份。我们得出结论，锥体终末突的基质是光感受器耦联的基础。红/绿锥体之间无差别地耦联，但蓝锥体很少与其他锥体连接。所有类型的锥体，包括蓝锥体，都与周围的视杆小球形成缝隙连接。
